extra money deducted on Apple music purchase

Do you see 2 different charges? A smaller charge and then a charge equal to the subscription cost?

Does the purchase show as paid on the account's purchase history ? Or are you only seeing : About payment card authorization holds from the App Store or iTunes Store - Apple Support ?

Is it likely to be as per that link ?

The smaller change is to test that the credit card is valid. The charge should be dropped and not completed.